Mouse Thymic Necrosis Virus (TA) is a murine herpesvirus first described by Rowe and Capps at the NIH in 1961. In neonatal mice, TA causes massive thymic necrosis with destruction of helper and cytotoxic T lymphocytes and acute immunosuprression. Older suckling and adult mice do not develop thymic necrosis but become perisitently infected. Virus can be isoloated from saliva and salivary glands for at least 6 months after infection. The prevalence of TA is unknown but infection may be widespread; in the only available estimate (published 1979), TA was detected in four of 15 mouse colonies. To help evaluate the significance of TA, a more broadly-based estimate of TA prevalence is proposed in this application. Possible long-term effects of this persistent virus infection on immune functions are unknown. Because mice are widely used in biomedical research and new drug screening, such effects in infected mice could compromise research and are therefore of great concern. TA might also be a prototype lymphotropic virus infection. T dependent immune function of chronically infected adult mice will be assessed throughout the animals" lifetime; tests of immune function will include induction of antibodies to sheep erythroycytes and keyhole limpet hemocyanin, delayed-type hypersensitivity, and tumor rejection. The lack of a cell culture assay has hindered work with TA. A culture system using thymocytes isolated from infected suckling mice was recently developed in this laboratory. Virus replication in these cells will be characterized. Extending promising preliminary results, requirements for infected thymocytes to productively infect other cell types, including lymphoma cells lines, and role of thymic epithelium, will be defined. Thymocyte subtypes expressing different major surface markers (Lyt antigens and maturational markers) will be fractionated and levels of virus in each subpopulation will be determined. Work to identify suitable cell lines for virus assay will also be done. Development of an enzyme immunoassay (ELISA) for TA antigen is also proposed. Although TA destroys T lineage lymphocytes, the virus persists in salivary gland. In this laboratory, TA was recently isolated from lactating mammary gland. Time course and duration of TA shredding from mammary gland will be defined, as will virus production in other glandular epithelial tissue (e.g., pancreas). Offspring raised by chronically infected mothers will be screened for TA in order to identify possible transmission.